Application of DC Generator and DC Motor

 

Applications of DC Generators

1. Separately-excited DC generator are rarely used in practical applications because of the additional expenses to be limit for the separate excitation supply.
2. DC shunt generator can be used for general purpose lighting and low-voltage DC supply system.
3. DC series generators do not find much application because of their rising voltage characteristics at higher loads, except these are sometimes used as boosters to compensate excessive voltage drops that can take place in a long DC feeder.
4. Flat compound DC generators are most commonly used for low-voltage DC distribution systems. Flat compound generators can also be used for charging of batteries since they can give fairly constant output terminal voltage, irrespective of load current.
5. Over-compound type DC generators can be used for lighting and general power supply applications because over-compounding can compensate for voltage drops in the distribution lines and thus voltage at the consumer end can be kept more or less constant.
6. Differentially-compound generators have a typical characteristic that their output voltage drops sharply with increase in load (output current). This feature is utilized for DC welding where the supply voltage between the two electrodes needs to be brought down sharply to avoid damage to the work piece once the arc has been established.

Applications of DC Motors

1. Shunt motors have low speed regulation, their does not change much from no-load to full load. Their torque is approximately proportional to the armature current. Shunt motors are used in applications requiring not too high starting torque with least requirements for speed variations such as centrifugal pumps, blowers, fans, lathes, machine tools, printing press, spinning and weaving machines, etc.
2. Series motors, on the other hand, have the exceptional feature of providing large torque at low speeds and have appreciably high starting torques. Power demand of a DC series motor automatically goes down at high loads due to sharp fall in its speed. Owing to these distinguishing features, series motors are used in traction, hoists, travel motion of cranes, conveyors, etc.
3. The characteristics of cumulative compound motor lies between those of shunt and series motors. It has a definite no-load speed like a shunt-motor, while its starting torque is relatively high, though not as high as a series motor, but definitely higher than a shunt motor, this type of motors are hence used in applications requiring high starting torque with less chance of speed variation such as plunger pumps, shears, crushers, punching presses, etc.
4. Differential compound motors are, however, rarely used in industries, and their applications are limited to experimental and research purpose only. The differential arrangement poses difficulties, especially at overloads and during starting. At overloads, the series flux may overpower the shunt flux, causing the total flux to be weakened drastically and even cause reverse rotation of the motor. At starting, if the armature currents rises too sharply, the series field may overpower the shunt field and cause the motor to start in a reverse direction. However, this problem can be overcome by keeping the series field winding shorted during the starting period of the motor.
5. Separately excited DC motors are most versatile in terms of speed control because of the provision for separate and independent control of field and armature circuits. For this reason, they are used in variable speed drives requiring wide range of speed variations either in forward or reverse directions. In addition, the speed control process is also very smooth. Separately excited DC motors find applications in paper mills, steel rolling mills, etc.